This project has as a final objective, the elucidation of those viral and host cell components which influence, at the molecular level, the phenomenon known as viral tropism. Currently, the emphasis of this project is focused on those components of measles virus which pertain to the neurotropism of this clinically relevant paramyxovirus. During the course of natural infection, neurotropic variants of measles virus are generated. Frequently, this gives rise to mild central nervous system involvement and, less frequently, to clinical encephalitis. In rare instances, a delayed encephalitis, subacute sclerosing parencephalitis, is observed. Although the mechanism(s) of this neurotropism is unknown, available evidence suggests that the viral envelope glycoproteins are involved and can be antigenically distinguished from the wild-type or vaccine strains using hybridoma antisera. Therefore, the initial phase of this project is to clone those genes encoding these proteins from a vaccine strain (Edmonston) of measles virus. From the nucleotide sequence, we will deduce the amino acid sequence of the proteins. To positively identify these clones, oligopeptides from the deduced amino acid sequence will be synthesized. Antisera raised against the synthetic peptides will then be used in a variety of immunologic techniques to identify the viral protein recognized and, thus, assign the clones. Once this is established, fragments of these cDNA clones will then be used as probes to identify their counterparts in neurotropic strains of measles virus presently available in our laboratory. The nucleotide and deduced amino acid sequence of the glycoproteins of the neurotropic strains will then be compared with the vaccine and wild-type virus for regions of homology and non-homology. The cloned glycoprotein genes will be placed in appropriate expression vectors to permit the study of their synthesis, regulation of expression, maturation and insertion into the host cell membrane.